TIME-DEPENDENT STRENGTH MOBILIZATION OF CLAY SEAMS EMBEDDED IN PROGRESSIVE ROCK SLOPE FAILURE PLANES

许多岩质边坡的破坏是由于岩石沿嵌有薄粘土煤层的滑动面滑动而发生的。通常不可能对从滑动面采集的未受干扰的薄粘土煤层进行三轴试验，因为试件的厚度不够大，不能放在三轴装置的底座上。对薄粘土试件进行剪切试验的唯一可能方法似乎是使用剪切箱试验，该试验传统上被认为是一种次要的试验方法，因为它的剪切机理简单。研究人员对实际岩质边坡破坏的粘土层试件进行了一系列的剪力箱试验，发现定容剪力箱试验可以给出合理的有效应力强度参数。他们从理论上推导了将剪力箱试验得到的强度换算成三轴试验强度的方法。在…分析中得到了成功的应用更多的岩质边坡破坏，导致了典型的强降雨触发的岩质边坡破坏机制的发现。然而，从实例研究的反分析中发现，用于边坡破坏分析的强度参数是零粘聚力，即使在剪切箱试验中实际观察到以有效应力表示的粘聚力的情况下也是如此。这种零粘聚力最终被发现是由于在偶尔的暴雨期间粘土煤层被淹没，经历了岩石边坡的渐进性破坏。从实用的角度来看，最重要的结论是，降雨不仅有效地诱发了滑动面内高水压引起的边坡破坏驱动力，而且还有效地降低了淹没引起的粘土层的粘聚力。这意味着在估算岩质边坡失稳的可能安全系数时，不应依赖于粘土层的粘聚力。较少

Many of the rock slope failures take place as the rock mass slide along the slip planes in which thin clay seams are embedded. It is not usually possible to carry the triaxial tests on the undisturbed thin clay seams taken from the slip planes because the thickness of the specimens is not large enough to set on the pedestal of the triaxial apparatus. The only possible way of carrying shear tests on the thin clay specimens seems to use the shear box test which traditionally considered as a minor testing method due to its simple mechanism of shear. The investigators have carried many series of shear box tests on the clay seam specimens taken from the actual rock slope failures and found that the constant volume shear box tests can give reasonable strength parameters in terms of effective stress. They have theoretically derived the method to convert the strength obtained from shear box tests into the strength obtained from triaxial tests. This was successfully utilized in the analyses of … More rock slope failures and resulted in the findings of mechanism of rock slope failures typically triggered by heavy intensive rainfall. The strength parameters to be applied to the slope failure analyses, however, were found from the back-analysis of case studies to be of zero cohesion even in the cases that some cohesion in terms of effective stress was actually observed ion the shear box tests. This zero-cohesion was eventually found to be resulted from the submersion of the clay seams undergoing the progressive rock slope failure during the period of occasional heavy rainfalls. The conclusion most important from the practical point of view is that the rainfall was found to be effective not only in inducing the driving force of slope failure by high water pressure in the slip planes but also in temporarily reducing the cohesion of the clay seams caused by submersion. This implies that we should not rely on the cohesion of the clay seams in estimating the possible factor of safety of rock slope failures. Less